Show a message when the test peripheral config is invalid.

Bug: 195491490
Test: run AudioLoopbackLatencyTest. verify valid and invalid
 test peripheral configs. i.e. a headset only, USB speakers + loopback plug...

Also, recombine (singular) AudioLoopbackBaseActivity and AudioLoopbackLatencyActivity classes.

Change-Id: I3568d9309af150f0e6c77f20c0ff56eed93801f5
4 files changed